This invention relates to a heat pump type air conditioning apparatus of the heat pump type capable of operating as a cooler and a heater, and more particularly to an improvement of an air conditioning apparatus utilizing a variable capacity type compressor.
To have a better understanding of this invention a prior art air conditioning apparatus of this type will firstly be described with reference to FIG. 1 of the accompanying drawing.
The air conditioning apparatus shown in FIG. 1 comprises an outdoor heat exchanger 1, a capillary tube 2 acting as a refrigerant expansion member, an indoor heat exchanger 3 and a variable capacity compressor 5 driven by an inverter, not shown, generating single phase or polyphase alternating current of a variable frequency, which are interconnected through a four way valve 7 and conduits 4, 6, 17 and 4a. Between the capillary tube 2 and the conduit 4a is disposed a bridge circuit 8 including parallelly connected first conduit 9, a second conduit 10 and a bypass conduit 11 provided with a variable throttle valve 12, for example an automatic expansion valve 12. At the time of cooling the refrigerant is permitted to flow through the capillary tube 2, first conduit 9, bypass conduit 11, a check valve 16 in the second conduit 10 and indoor heat exchanger 3, whereas at the time of heating, the refrigerant is permitted to flow through the indoor heat exchanger 3, a check valve 14 of the first conduit 9, bypass conduit 11, a check valve 12, capillary tube 2, pairs of check valves 13, 14 and 15, 16 included in the first and second conduits 9 and 10 respectively. A compressor cooling conduit, for example a liquid refrigerant bypass conduit 17 is connected between a junction 4b between the capillary tube 2 and the bridge circuit 8 and the suction conduit 6a of the compressor 5. The liquid refrigerant bypass conduit 17 includes a capillary tube 18. The liquid refrigerant bypass conduit 17 can be substituted by a liquid injection conduit which injects low temperature liquid refrigerant into the compressor 5.
With the construction described above when the four way valve 7 is rotated to a position shown in FIG. 1, the refrigerant flows in a circuit shown by solid line arrows to effect cooling operation. The automatic expansion valve 12 in the bridge circuit 8 automatically changes its degree of opening so as to make the quantity of the circulating refrigerant to be proportional to the output of the compressor 5. More particularly, when the output of the compressor 5 is large the quantity of the circulating refrigerant is made large, whereas when the output of the compressor 5 is small, the quantity of the circulating refrigerant is made small.
In the prior art air conditioning apparatus described above, since the load of the compressor 5 is small when its output is small, the quantity of the liquid refrigerant supplied to the compressor through the bypass conduit 17 for cooling the same may be small. However, under this condition, as the degree of opening of the automatic expansion valve 12 is small, the quantity of the refrigerant supplied to the liquid refrigerant bypass conduit 17 increases proportionally. For this reason, the compressor 5 would be cooled excessively so that the refrigerant in the compressor 5 will dissolve into lubricant utilized to lubricate the moving or rotating parts of the compressor, thus decreasing the lubricating performance. Furthermore, the automatic expansion valve 12 is expensive which increases the cost of the air conditioning apparatus.